Wireless local area networks (WLANs) use infrared (IR) or radio frequency (RF) communications channels to communicate between portable or mobile computer terminals and stationary access points or base stations. These access points are connected by a wired or wireless communication channels to a network infrastructure which connects groups of access points together to from a local area network (LAN), which can include one or more host computers. In turn, the LAN can be connected to another larger network such as the Internet and the World Wide Web (Web). Several protocols, including the IEEE 802.11 standard, “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications” have been designed to standardize WLAN communications. Such standardization is useful for optimizing user requirements, including interoperability, spatial layout, response time, loading and throughput requirements of the network.
“Roaming” terminals are mobile units that can associate with any stationary access point (SAP) in range within a WLAN, and may seamlessly move from SAP to SAP. Each roaming terminal analyzes received signals from access points in its vicinity and associates with a single access point. Communication with an access point connects a terminal with the LAN and therefore with external networks such as the Internet. The region around an access point can be referred to as a “cell”. Roaming terminals can move from cell to cell and remain connected to the LAN and any other network to which the roaming terminal is connected.
The IEEE 802.11 standard defines as the frequencies or channels used for WLAN communications. Typically, a SAP must be manually configured to a particular set of frequency channels for use in a frequency hopping or direct sequence spread spectrum (DSSS) modulation technique. For example, in the 802.11b DSSS standard, there are three non-interfering channels spaced 25 MHz apart in the 2.4 GHz band (channels 1,6, and 11 in Table 1 hereunder). Multiple IEEE 802.11b networks may operate in the same area by suitable section of the channel for each SAP. This channel configuration is normally set manually by the user or by factory default. Such techniques are disadvantageous since the manually setting of channels, or the selection and installation of factory-set SAPs at particular locations, is error prone. Moreover, even if configured correctly on installation, the selected installation pattern and frequency designations may not be optimal at all times due to data traffic, interference, or other time-dependent conditions during actual use.
Often times there can be several unrelated WLANs or “Extended Service Sets” belonging to different entities in a dense area such as an office building. The SAPs of these unrelated WLANs may use the same frequencies in close proximity. Therefore it is possible for a roaming unit associated with one WLAN to encounter interference with a communication link on an unrelated WLAN. This situation is not desirable. Thus, it is desirable for the SAPs to be able to implement an the optimum pattern or distribution of channel frequencies and have the ability to switch between channels to utilize the best communication link with the nearest available SAP.